Let's start! Boil the potatoes in a pot with plenty of water until a fork passes all the way through. Once they are ready drain the water, and peel the potatoes while they are still warm so the skin peels easily. Cut them in half and then in big chunks, about 4cm thick. Put them in a bowl together with the chopped onions, the capers and dill. Cover, and put in the fridge to cool down. Make the sauce by blending all the ingredients together until the mixture becomes creamy. Set aside.In a small frying pan put the teaspoon of olive oil and heat. Add the slice of the smoked mackerel and seer until it forms a crust. Add the lemon juice and let it seer for half a minute. Take the potato mix from the fridge and add 2/3 of the sauce and mix well to coat evenly. Put the slice of fish on top and drizzle the remaining sauce over it. If you want you can cut the fish in small pieces and mix in the salad. Enjoy!